Such clamping elements have been known in vastly different embodiments and for vastly different tasks. For example, a tensioning element, which is not only able to hold electronic boards of varying size in a vibration-free flat position, but also guarantees vibration-free mounting in the case of arrangement of the tensioning elements in empty places of the board, has become known from German Patent Specification No. DE-PS 37,32,346. To achieve this, a concept has been created in which a U-shaped guide rail is provided for receiving via a holding eye arranged in its center and a clamping element pulled through this eye. This embodiment has proved to serve its purpose well, but is far too inefficient in terms of its thermal conductivity in the housing rack, which is force-cooled by so-called heat exchangers (cold plates), especially at the interfaces between the electronic board and the wall of the rack housing.
Commercially available clamping element designs provide for various mechanical clamp forms between electronic boards and housing racks, e.g., clamping clips made of spring steel, which are inserted into the correspondingly shaped board holding groove of the cold plate. The heat transfer from the board to the housing wall is also accomplished by these spring clips.
Furthermore, so-called eccentric clamping devices have also been known, in which a small spring plate and an eccentric element press the web of the electronic board, thus establishing the connection and heat conduction between the board and the heat exchange wall. Aside from the fact that a special processing of the cold plate is necessary only for the mounting of the eccentric and the spring in this case as well, the heat dissipation is also much lower.
Further heat-conducting clamping elements of complicated design, which are provided with separate control members or additionally coupled components, have been known from German Offenlegungsschriften Nos. DE-OS 35,22,124 and DE-OS 32,45,072.
All these prior-art embodiments have a number of disadvantages. For example, longitudinal flow of the coolant takes place in the cold plates or heat exchangers, which leads to different temperatures within the rack and to decreasing cooling capacity from one electronic board to the next, because the coolant is being continuously heated by the addition of heat (FIG. 1).
However, the prior-art clamping elements are also insufficient for adequate heat conduction or dissipation due to their relatively small, only linear or punctiform contact areas or cross-sectional areas. In addition, the clamping force, which is essential for the thermal resistance over the pressed contact surfaces, is usually subject to great tolerances, so that a uniform, defined clamping force can be set only by means of special measuring devices, torque wrenches, etc.